GB609797A - Improvements in or relating to the production of artificial films - Google Patents

Abstract

A synthetic linear polymeric ester, obtained by heating one or more glycols of the formula HO.(CH2)n.OH, where n is an integer greater than 1 but not greater than 10, with terephthalic acid or an ester-forming derivative thereof, is melted and the molten polymer is formed into a thin layer which is rapidly cooled to form a solid film. The film may be molecularly oriented longitudinally or laterally by drawing, rolling, stamping or similar operation. Ethylene, trimethylene, tetramethylene, hexamethylene or decamethylene glycol may be esterified with terephthalic acid or its aliphatic, cycloaliphatic, or aryl esters, or its acid halides, or ammonium or amine salts. The molten polymer may be cooled by air, water, or other inert fluid, or by a high melting metal surface. Films may be formed by pouring the molten polymer on to a flat metal tray and cooling by means of air. The polymer may be extruded through a slot orifice and the film may be cooled on extrusion by jets of cold inert gas, immersion in an inert liquid, or by contact with a metal surface which is itself cooled by jets of a cold fluid or by immersion in a liquid. The polymer may be extruded in the form of a large diameter tube with thin walls and the tube may be slit and rolled out to form a sheet. The films may be stretched after extrusion while they are being quenched. After quenching, the films are transparent. They may be rendered opaque by heating so as to induce crystallization. They may be drawn, rolled, or stamped, after quenching. The shrinkability may be reduced by subjecting the films to a temperature higher than the temperature at which they have been drawn, and while they are under tension. In an example, polyethylene terephthalate is heated in nitrogen to 285 DEG C. and the molten polymer is forced through a filter pack of sand and stainless steel gauze, and through a slot orifice. The ribbon of molten polymer is passed into a quenching bath of cold water through pinch rolls which stretch the film and pass it to a winding reel. The film is then passed to a stretching machine consisting of two pairs of pinch rolls, take-off reel and winding reel. The apparatus is enclosed in a mineral oil bath heated to 70 DEG C. The resiliency of the stretched film is increased by heating it under tension in mineral oil at 200 DEG C. The films have high tensile strength, high dielectric strength, high resistance to acids and organic liquids, good weathering properties, and high resistance to attack by insects and bacteria. They may be used for wrapping material, insulating material, clothing and curtains. A drawn film which has not been heat set may be wrapped round an article, the edges may be heat sealed, and then the closed package may be shrunk on to the wrapped article by heating. The films may be produced in tubular form. Specifications 542,509, 567,358 and 578,079 are referred to.